docs: def _iter_lexerclasses(plugins=True):
      """Return an iterator over all lexer classes."""
      for key in sorted(LEXERS):
          module_name, name = LEXERS[key][:2]
          if name not in _lexer_cache:
              _load_lexers(module_name)
          yield _lexer_cache[name]
      if plugins:
          for lexer in find_plugin_lexers():
              yield lexer